Genetic Biodiversity


  • Heredity is the passing on of characteristics from an individual to its offspring (babies).


  • The basic unit of heredity is the gene. A gene is a specific length of DNA on a chromosome that has information to create a protein that determines a characteristic (eg hair or eye colour). Alternative forms of genes are alleles (eg one allele gives brown hair and one allele gives blonde hair).


  • The genotype is the genetic makeup of an individual for a characteristic. The physical expression (what you look like) is the phenotype. A phenotype can be changed by the environment (eg sun turning your skin colour darker).


  • Genetic biodiversity describes the range of different genes and alleles in a population. Members of a species are usually in populations so share a common gene pool.


  • A gene pool is made up of all the alleles of all the genes that exist in a population at any one time. Each population has a slightly different gene pool.


  • The number of each allele in the gene pool of a population is called the allele frequency. (eg in a classroom of 25 people with two alleles for hair colour H and h. There would be 50 alleles in total (25 x 2). H occurs 22 times, h occurs 28 times. The frequency of the H allele is 0.44 (22/50) and 0.56 for the h allele).


  • The greater the number of different alleles present,the greater the genetic biodiversity. This is important for the survival of a species as there is more material for evolution to act on. When the environment changes, the chance for favourable alleles is high so individuals with the necessary adaptations for the new environment is high.


  • However in farms and orchards, the animals and plants (eg banana) are clones of just a few favourable individuals. If the environment changes it is more likely that this gene pool won't have the alleles to cope with the change.


  • Allele frequencies in a gene pool is changing as individuals are born and die. Immigration also changes frequency. 


  • If a gene has only one allele, it is said to be fixed and its frequency is 100% or 1 (eg the coat colour gene in horses is only one allele B, therefore it's frequency is 1).
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